如何围绕对角线旋转 CALayer？

Question

我正在尝试实现一个翻转动画，以便在 iPhone 应用程序等棋盘游戏中使用。动画应该看起来像一个旋转并改变其背面颜色的游戏块（有点像Reversi piece）。我已经设法创建了一个动画，它围绕其正交轴翻转作品，但是当我尝试通过改变围绕 z 轴的旋转来围绕对角轴翻转它时，实际图像也会旋转（不足为奇）。相反，我想围绕对角轴“按原样”旋转图像。

我尝试更改layer.sublayerTransform，但没有成功。

这是我当前的实现。它通过一个技巧来解决在动画结束时获取镜像图像的问题。解决方案是不实际将图层旋转 180 度，而是将其旋转 90 度，更改图像然后将其旋转回来。

最终版本：根据 Lorenzos 的建议创建离散键控动画并计算每一帧的变换矩阵。此版本尝试根据图层大小估算所需的“引导”帧数，然后使用线性键控动画。此版本以任意角度旋转，因此围绕对角线旋转使用 45 度角。

示例用法：

[someclass flipLayer:layer image:image angle:M_PI/4]

实施：

- (void)animationDidStop:(CAAnimationGroup *)animation
                finished:(BOOL)finished {
  CALayer *layer = [animation valueForKey:@"layer"];

  if([[animation valueForKey:@"name"] isEqual:@"fadeAnimation"]) {
    /* code for another animation */
  } else if([[animation valueForKey:@"name"] isEqual:@"flipAnimation"]) {
    layer.contents = [animation valueForKey:@"image"];
  }

  [layer removeAllAnimations];
}

- (void)flipLayer:(CALayer *)layer
            image:(CGImageRef)image
            angle:(float)angle {
  const float duration = 0.5f;

  CAKeyframeAnimation *rotate = [CAKeyframeAnimation
                                 animationWithKeyPath:@"transform"];
  NSMutableArray *values = [[[NSMutableArray alloc] init] autorelease];
  NSMutableArray *times = [[[NSMutableArray alloc] init] autorelease];
  /* bigger layers need more "guiding" values */
  int frames = MAX(layer.bounds.size.width, layer.bounds.size.height) / 2;
  int i;
  for (i = 0; i < frames; i++) {
    /* create a scale value going from 1.0 to 0.1 to 1.0 */
    float scale = MAX(fabs((float)(frames-i*2)/(frames - 1)), 0.1);

    CGAffineTransform t1, t2, t3;
    t1 = CGAffineTransformMakeRotation(angle);
    t2 = CGAffineTransformScale(t1, scale, 1.0f);
    t3 = CGAffineTransformRotate(t2, -angle);
    CATransform3D trans = CATransform3DMakeAffineTransform(t3);

    [values addObject:[NSValue valueWithCATransform3D:trans]];
    [times addObject:[NSNumber numberWithFloat:(float)i/(frames - 1)]];
  }
  rotate.values = values;
  rotate.keyTimes = times;
  rotate.duration = duration;
  rotate.calculationMode = kCAAnimationLinear;

  CAKeyframeAnimation *replace = [CAKeyframeAnimation
                                  animationWithKeyPath:@"contents"];
  replace.duration = duration / 2;
  replace.beginTime = duration / 2;
  replace.values = [NSArray arrayWithObjects:(id)image, nil];
  replace.keyTimes = [NSArray arrayWithObjects:
                      [NSNumber numberWithDouble:0.0f], nil];
  replace.calculationMode = kCAAnimationDiscrete;

  CAAnimationGroup *group = [CAAnimationGroup animation];
  group.duration = duration;
  group.timingFunction = [CAMediaTimingFunction
                          functionWithName:kCAMediaTimingFunctionLinear];
  group.animations = [NSArray arrayWithObjects:rotate, replace, nil];
  group.delegate = self;
  group.removedOnCompletion = NO;
  group.fillMode = kCAFillModeForwards;
  [group setValue:@"flipAnimation" forKey:@"name"];
  [group setValue:layer forKey:@"layer"];
  [group setValue:(id)image forKey:@"image"];

  [layer addAnimation:group forKey:nil];
}

原码：

+ (void)flipLayer:(CALayer *)layer
          toImage:(CGImageRef)image
        withAngle:(double)angle {
  const float duration = 0.5f;

  CAKeyframeAnimation *diag = [CAKeyframeAnimation
                               animationWithKeyPath:@"transform.rotation.z"];
  diag.duration = duration;
  diag.values = [NSArray arrayWithObjects:
                 [NSNumber numberWithDouble:angle],
                 [NSNumber numberWithDouble:0.0f],
                 nil];
  diag.keyTimes = [NSArray arrayWithObjects:
                   [NSNumber numberWithDouble:0.0f],
                   [NSNumber numberWithDouble:1.0f],
                   nil];
  diag.calculationMode = kCAAnimationDiscrete;

  CAKeyframeAnimation *flip = [CAKeyframeAnimation
                               animationWithKeyPath:@"transform.rotation.y"];
  flip.duration = duration;
  flip.values = [NSArray arrayWithObjects:
                 [NSNumber numberWithDouble:0.0f],
                 [NSNumber numberWithDouble:M_PI / 2],
                 [NSNumber numberWithDouble:0.0f],
                 nil];
  flip.keyTimes = [NSArray arrayWithObjects:
                   [NSNumber numberWithDouble:0.0f],
                   [NSNumber numberWithDouble:0.5f],
                   [NSNumber numberWithDouble:1.0f],
                   nil];
  flip.calculationMode = kCAAnimationLinear;

  CAKeyframeAnimation *replace = [CAKeyframeAnimation
                                  animationWithKeyPath:@"contents"];
  replace.duration = duration / 2;
  replace.beginTime = duration / 2;
  replace.values = [NSArray arrayWithObjects:(id)image, nil];
  replace.keyTimes = [NSArray arrayWithObjects:
                      [NSNumber numberWithDouble:0.0f], nil];
  replace.calculationMode = kCAAnimationDiscrete;

  CAAnimationGroup *group = [CAAnimationGroup animation];
  group.removedOnCompletion = NO;
  group.duration = duration;
  group.timingFunction = [CAMediaTimingFunction
                          functionWithName:kCAMediaTimingFunctionLinear];
  group.animations = [NSArray arrayWithObjects:diag, flip, replace, nil];
  group.fillMode = kCAFillModeForwards;

  [layer addAnimation:group forKey:nil];
}

Answer 1

你可以这样伪造它：创建一个仿射变换，沿着它的对角线折叠图层：

A-----B           B
|     |          /
|     |   ->   A&D
|     |        /
C-----D       C

更改图像，并将 CALayer 转换回另一个动画中。 这将产生图层围绕其对角线旋转的错觉。

如果我没记错数学的话，矩阵应该是：

0.5 0.5 0
0.5 0.5 0
0   0   1

更新： 好的，CA 不太喜欢使用退化变换，但你可以这样近似：

CGAffineTransform t1 = CGAffineTransformMakeRotation(M_PI/4.0f);
CGAffineTransform t2 = CGAffineTransformScale(t1, 0.001f, 1.0f);
CGAffineTransform t3 = CGAffineTransformRotate(t2,-M_PI/4.0f);  

在我在模拟器上的测试中仍然存在问题，因为旋转发生的速度比 te 平移发生得快，所以使用纯黑色方块时效果有点奇怪。我想如果你有一个围绕它的透明区域的居中精灵，效果将接近预期的效果。然后，您可以调整 t3 矩阵的值，看看是否得到更有吸引力的结果。

经过更多研究，似乎应该通过关键帧为其自己的过渡设置动画，以获得对过渡本身的最大控制。假设你要在一秒钟内显示这个动画，你应该使用 kCAAnimationDiscrete 制作十个矩阵，每十分之一秒显示一次，而不需要插值；这些矩阵可以通过以下代码生成：

CGAffineTransform t1 = CGAffineTransformMakeRotation(M_PI/4.0f);
CGAffineTransform t2 = CGAffineTransformScale(t1, animationStepValue, 1.0f);
CGAffineTransform t3 = CGAffineTransformRotate(t2,-M_PI/4.0f);  

keyFrame 的 ech 的 animationStepValue 取自这个进程：

{1 0.7 0.5 0.3 0.1 0.3 0.5 0.7 1}

也就是说：您正在生成十个不同的变换矩阵（实际上是 9 个），将它们作为关键帧推送到每十分之一秒显示一次，然后使用“不插值”参数。您可以调整动画数量以平衡平滑度和性能*

*抱歉可能出现错误，最后一部分是在没有拼写检查的情况下编写的。

Answer 2

我解决了。您可能也已经有了解决方案，但这是我发现的。真的很简单……

你可以使用CABasicAnimation来做对角线旋转，但它需要是两个矩阵的串联，即层的现有矩阵，加上一个CATransform3DRotate。 “诀窍”是，在 3DRotate 中，您需要指定要旋转的坐标。

代码如下所示：

CATransform3DConcat(theLayer.transform, CATransform3DRotate(CATransform3DIdentity, M_PI/2, -1, 1, 0));

这将使旋转看起来好像正方形的左上角围绕轴 Y=X 旋转，并移动到右下角。

动画代码如下所示：

CABasicAnimation *ani1 = [CABasicAnimation animationWithKeyPath:@"transform"];

// set self as the delegate so you can implement (void)animationDidStop:finished: to handle anything you might want to do upon completion
[ani1 setDelegate:self];

// set the duration of the animation - a float
[ani1 setDuration:dur];

// set the animation's "toValue" which MUST be wrapped in an NSValue instance (except special cases such as colors)
ani1.toValue = [NSValue valueWithCATransform3D:CATransform3DConcat(theLayer.transform, CATransform3DRotate(CATransform3DIdentity, M_PI/2, -1, 1, 0))];

// give the animation a name so you can check it in the animationDidStop:finished: method
[ani1 setValue:@"shrink" forKey:@"name"];

// finally, apply the animation
[theLayer addAnimation:ani1 forKey@"arbitraryKey"];

就是这样！该代码会将正方形（theLayer）旋转 90 度并垂直于屏幕呈现自身，使其不可见。然后，您可以更改颜色，并执行完全相同的动画将其恢复。相同的动画效果是因为我们连接了矩阵，所以每次你想旋转时，只需这样做两次，或者将M_PI/2 更改为M_PI。

最后，应该注意的是，这让我发疯了，完成后，除非您明确将其设置为动画结束状态，否则图层将恢复到其原始状态。这意味着，就在您想要添加的 [theLayer addAnimation:ani1 forKey@"arbitraryKey"]; 行之前

theLayer.transform = CATransform3DConcat(v.theSquare.transform, CATransform3DRotate(CATransform3DIdentity, M_PI/2, -1, 1, 0));

在动画完成后设置它的值。这将防止快速恢复到原始状态。

希望这会有所帮助。如果不是你，那么也许是其他人像我们一样用头撞墙！ :)

干杯，

克里斯

Answer 3

这是一个 Xamarin iOS 示例，我用它来拍打方形按钮的角，就像一只狗耳朵（很容易移植到 obj-c）：

方法 1： 对 x 和 y 轴使用带有 1 的旋转动画（Xamarin.iOS 中的示例，但很容易移植到 obj-c）：

// add to the UIView subclass you wish to rotate, where necessary
AnimateNotify(0.10, 0, UIViewAnimationOptions.CurveEaseOut | UIViewAnimationOptions.AllowUserInteraction | UIViewAnimationOptions.BeginFromCurrentState, () =>
{
    // note the final 3 params indicate "rotate around x&y axes, but not z"
    var transf = CATransform3D.MakeRotation(-1 * (nfloat)Math.PI / 4, 1, 1, 0);
    transf.m34 = 1.0f / -500;
    Layer.Transform = transf;
}, null);

方法2：只需将x-axis 旋转和y-axis 旋转添加到CAAnimationGroup，这样它们就可以同时运行了：

// add to the UIView subclass you wish to rotate, where necessary
AnimateNotify(1.0, 0, UIViewAnimationOptions.CurveEaseOut | UIViewAnimationOptions.AllowUserInteraction | UIViewAnimationOptions.BeginFromCurrentState, () =>
{
    nfloat angleTo = -1 * (nfloat)Math.PI / 4;
    nfloat angleFrom = 0.0f ;
    string animKey = "rotate";

    // y-axis rotation
    var anim = new CABasicAnimation();
    anim.KeyPath = "transform.rotation.y";
    anim.AutoReverses = false;
    anim.Duration = 0.1f;
    anim.From = new NSNumber(angleFrom);
    anim.To = new NSNumber(angleTo);

    // x-axis rotation
    var animX = new CABasicAnimation();
    animX.KeyPath = "transform.rotation.x";
    animX.AutoReverses = false;
    animX.Duration = 0.1f;
    animX.From = new NSNumber(angleFrom);
    animX.To = new NSNumber(angleTo);

    // add both rotations to a group, to run simultaneously
    var animGroup = new CAAnimationGroup();
    animGroup.Duration = 0.1f;
    animGroup.AutoReverses = false;
    animGroup.Animations = new CAAnimation[] {anim, animX};
    Layer.AddAnimation(animGroup, animKey);

    // add perspective
    var transf = CATransform3D.Identity;
    transf.m34 = 1.0f / 500;
    Layer.Transform = transf;

}, null);